In 1990, when climatologist Konrad Steffen established Swiss Camp, one of the first automatic weather stations on Greenland's ice sheet, global warming wasn't high on his agenda. Steffen wanted to study the interaction of ice and atmosphere at the "equilibrium line," the altitude where summer melt and winter snowfall are historically in perfect balance. "We probably have more information on nearby planets than we do on Greenland," he says. "Parts of Greenland have never been measured, because few satellites can see that latitude, and those that can haven't been up long enough. And it's difficult to deploy surface instruments in those conditions." Steffen's aim was to begin filling in gaps in scientists' understanding of the processes that drive -- and are affected by -- changes on the vast body of ice that holds roughly eight per cent of the world's freshwater supply.

But near the Earth's poles, equilibrium isn't what it used to be. A few years after Steffen built his research station, he noticed that temperatures on Greenland's ice cap were rising -- and then rising faster. Over a decade, the average winter temperature shot up 6 degrees C, an increase so improbable that at first he declined to publish it, fearing an error in his calculations.

-snip-

It can't be easy to herald a potential planet-wide catastrophe. But despite all the bleak data being mined from Steffen's network, he says he is enjoying his work more than ever. "For one thing," he says, "people are starting to listen, to pay attention to science. Even politicians are starting to understand that we have a higher level of CO2 in the atmosphere than at any time in the past 600,000 years, and that our future depends on whether we can get greenhouse-gas emissions under control.

"We are at a fork in the road," he says. "We could take action now and reduce our carbon footprint. That doesn't mean reducing our standard of living or going backward. We can move forward, but in more efficient ways. We can still make money by building and selling the cleanest technology possible. But if we continue to build coal plants and sell them to China and India, then we are thinking short-term; we are not thinking of our children." This year, Steffen will add two weather stations to his network, as well as more GPS and seismic instruments to record ice quakes. He will also attempt to climb down into a moulin, a vertical shaft that channels rushing meltwater down to the bedrock. If all goes well, he'll install laser instruments that may lead to a new understanding of the dynamics of ice-sheet plumbing.

Both Steffen and Zwally suspect moulins, which move meltwater and the heat it carries almost a mile through the ice, have a significant effect on the health of ice caps and, by extension, on climate change.

"We call this 'dynamic response,''" Steffen says. "What happens is that the melting accelerates as meltwater funnels down to the bedrock. At the bottom, the water acts as a lubricant, flowing under the outlet glaciers and allowing the ice to slip into the sea more quickly. We hadn't expected ice sheets could react to warming so quickly. That is the kind of feedback we are coming to understand in the Arctic; it's a very sensitive environment." The acceleration could be a short-term adjustment to the warmer temperatures, Steffen says, or it might last much longer. But some scientists, including lead NASA climatologist James Hansen, believe Zwally and Steffen's observations, coupled with new data from Antarctica, suggest a major polar melt may be commencing. They point to a phenomenon called the albedo effect, in which melting ice exposes more land and water, causing the Earth's surface to become less reflective, and to absorb more of the sun's energy.

In a 2005 article in the scientific journal Climate Change, Hansen wrote that the current pace of melting, driven by the buildup of greenhouse gases in the atmosphere, could lead to a self-reinforcing and perhaps unstoppable cycle of feedback that could result in the total disintegration of the Greenland ice sheet. Hansen and many other climatologists believe it is likely the Greenland ice sheet will begin melting uncontrollably if global temperatures climb more than 2 degrees C. A rapid meltdown in Greenland would quickly raise sea levels and flood coastal cities and farms. As well as sending large icebergs down the coast, the infusion of cold, fresh water could disrupt ocean currents such as the Gulf Stream, which help to regulate the weather in the North Hemisphere."If that feedback kicks in," says Steffen, "then the average person will worry." But because dynamic response is so poorly understood, it has not yet been incorporated into the numerical models that climatologists use to project sea-level changes. For this reason, the potential influence of dynamic response on sea-level rise wasn't factored into the sea-level projections in the Climate Change 2007 report that the IPCC released earlier this year. A consensus of hundreds of scientists from 40 countries, the IPCC report concludes that the warming of the climate "is unequivocal," as evidenced by rising temperatures, widespread melting of snow and ice, and rising sea levels.

<snip>"Dynamic response is the elephant in the room," says Martin Truffer of the University of Alaska's Geophysical Institute. "We know well enough that there's likely to be a higher sea-level rise than the IPCC was willing to project. They are trying to be cautious and conservative. But their conclusions lag behind the latest findings." Over dinner, I press Steffen to make a rough prediction on sea-level rise by 2100. "Unfortunately," he says, somewhat hesitantly, "I think we are looking at more like a metre." A one-metre rise over the next 93 years would flood low-lying coastal areas and megadeltas, such as the Nile and South Asia's Brahmaputra, where millions live.

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